In Honor of Fessenden and Heising
The early history of wireless contains the names of many great pioneers. While Marconi’s name is most well known, the names of Fessenden and Heising are only rarely mentioned.
As early as 1900 Reginald Fessenden was experimenting with the direct transmission of human speech. While during WW1, Raymond Heising was developing a method of constant-current modulation that was one of the earliest forms of AM.
Since I have been one of the active CW 600m stations as part of the ARRL’s Experimental License project for some time now, I decided to take a step or two further into the realm of early radio transmissions. One of the transmitters I have used for 600m CW and QRSS work has been a vintage homebrew design that could support traditional CW and Heising AM. Since the ARRL’s Part 5 license only supports CW and narrow-band digital modes, the Heising modulator went unused until a new idea came to mind.
Fessenden’s early work includes a very unique 1906 Christmas Eve transmission of him playing the violin, a recording of a “Ombra mai fu”, and him reading a Bible verse. An idea was thus born to apply for an FCC STA (Special Temporary Authorization) for 600m operation that is for amplitude modulation, in particular the Heising modulation. With the cooperation of commercial coastal CW station WNE and the FCC’s OET (Office of Engineering Technology) the STA with call sign WF9XIH was granted for AM transmissions until March 1st, 2012 with a center carrier frequency of 472.5kHz. The plan is to begin a series of evening test transmissions the week of December 18th, 2011 with a special recreation of Fessenden’s Christmas Eve transmission at 0200z on Dec 25th. (That would be 9pm EST Dec 24th, 2011).
Since the likelihood of a 5w AM signal being heard much beyond a few 10’s of miles, a 500W solid state linear PA will be used for best DX. WF9XIH is licensed for up to 20wERP (just like the WD2XSH stations) and every effort will be made to run as close to that ERP as possible. The same antenna (a 160m dipole feed as a Marconi-T against ground) that has been used for WD2XSH/31 will be used for WF9XIH.
Commercial station WNE is currently running CW marine weather transmissions at 2200z & 0100z daily. So you can sharpen your 25WPM CW skills at those times too. WF9XIH transmissions are being coordinated with WNE and any changes to the WNE schedule will alter the WF9XIH operating times.
The current plan is to at least make a Heising AM transmission most evenings at 0200z. Audio loops of speech and a series of stepped audio tones will be used most of the time. The stepped audio tones will make it easier for DX listeners to demodulate in CW or SSB mode even when they are well beyond the range of the AM signal.
Information about WD2XSH/31 can be found at: http://w4dex.com/500khz/wd2xsh31.htm
If you copy any of the transmissions, please be sure to log them at www.500kc.com
Extra effort will be made to try and be QRV in the evenings the week before and after the Christmas weekend.
Brian Justin, WA1ZMS/4 & WD2XSH/31 & WF9XIH